The invention relates to a pump system for delivering cryogenic liquids with a container for receiving cryogenic liquid and at least one reciprocating pump that is arranged in the container in such a way that it can be immersed in the cryogenic liquid.
To deliver cryogenic liquids at temperatures of below xe2x88x92200xc2x0 C., to date generally one-cylinder pumps that are inserted from above into an insulating vessel are used. For reasons of installation technology, the discharge of the feeder stream is carried out via this upper pump installation opening in the insulating vessel. Filling the vessels with the media to be delivered is carried out in most cases by a large storage tank, whereby determining the maximum filling height in these vessels is found by expansion pipes (sounding pipes) or content displays. The control of the maximum filling height is carried out in most cases manually or by a contact that is triggered by the liquid, by which a solenoid valve is actuated in the gas feed or exhaust line. Since the pumps cannot be operated without sub-cooling the feeder liquid, these large-volume vessels have a pressure buildup device by which the feeder liquid can be sub-cooled within a short time.
Since especially hydrogen in liquefied form is becoming increasingly more important and motor vehicles are already operated with hydrogen, it is necessary to provide suitable pumps for refueling these motor vehicles.
The known pumps may be suitable for laboratory experiments with small feeder streams and large reliable pressure pulsations; for a quick, pulsation-free liquid refueling of motor vehicles, however, this type of pump is unsuitable. In addition, such xe2x80x9cgas station pumpsxe2x80x9d must always be ready for use (cold-start) so that by the structurally necessary compact type of design in the known pumps, an enormous flow of heat into the liquid to be delivered takes place and the liquid sub-cooling that is necessary for the function is quickly withdrawn.
The object of this invention is to make available a pump system of the above-mentioned type with which larger amounts of cryogenic liquids, especially also liquid hydrogen, can also be delivered economically and reliably.
This object is achieved according to the invention in that the reciprocating pump has a connecting rod that is connected to the plunger, which is brought out from the container so that tensile forces can be applied from outside, and the connecting rod is provided with a return spring in such a way that the plunger can be returned to a starting position opposite the pressure stroke.
Several such pumps that are connected on the pressure side to a common pressure housing are suitably inserted in the container. Because of the possibility of individual installation and the pumps that operate on suction, the cross-sections that are relevant for heat conduction at the pumps and at the container are kept very small, by which only a very small input of heat into the container liquid is carried out. For further reduction of heat input in the container, the connecting rod is preferably brought out from the container via a seal. In the case of the especially practical solution, according to which the pump is used from above in the container, the connecting rod is brought out from the container via a heat-insulated container neck. To further reduce the gas heat conduction, an insulating cartridge can be provided in the neck of the container. In addition, the container is advantageously vacuum-insulated.
According to an especially preferred embodiment of the invention, the pump cylinder of the reciprocating pump is divided by the plunger into a pressure side and an induction side, whereby the plunger has a plunger body as well as a movable plunger ring that is brought to rest on the plunger body when the plunger moves in the direction opposite the pressure stroke in such a way that a gap is formed that produces a connection between the pressure side and the induction side and closes the gap when the plunger moves in the pressure stroke.
On the pressure-side end of the pump cylinder, a spring-loaded exhaust valve is provided. In addition, on the induction-side end of the pump cylinder, a bottom valve is arranged that can be actuated by means of the connecting rod in such a way that it opens on the pressure stroke and is closed when the stroke reverses.
Also, at the pressure-side end of the pump cylinder, a seal is suitably arranged to seal the connecting rod relative to the pump housing, which has a valve that can be actuated by the connecting rod, and said valve is closed when tensile forces are exerted on the connecting rod and is opened when the connecting rod returns under the action of the spring.
The pump system according to the invention can advantageously be used for a whole series of applications. In connection with a corresponding swash plate drive that is arranged outside of the container and that is connected with the connecting rods to the individual reciprocating pumps, the number as well as the diameter of the individual pumps in a common pressure housing vary greatly, so that the pumps according to this design principle can be matched to virtually all required deliveries with minimal pressure pulsation. Because of the merits of this pump design relative to the previous design, the use of such pumps is also conceivable as an aircraft pump in the new generation of hydrogen-driven aircraft. Because of the small masses of the pump system, the cooling losses are Very low. By the very simple design structure, a very reasonably priced, reliable and technically high-quality pump is made available.